(1) Field of the Invention
The invention relates to methods of detecting targets, particularly (although not exclusively) by use of a radar or similar system.
(2) Description of the Art
One application of radar systems is in the field of area monitoring, in which detection of targets within a certain area is required. For example, it may be required to detect the presence of intruders within a monitored area. Examples of radar systems suitable for performing this type of function are described in U.S. Pat. Nos. 4,595,924 and 6,466,157 and in published US patent application 2002/0 060 639.
A common problem encountered in target detection using radar is that small objects can be difficult to detect in the presence larger clutter returns. For example, intruders close to fixed objects such as building, walls, fences etc, or small objects lying on the ground (e.g. debris on a runway) may not be detected due to large clutter returns from the surrounding environment. Several methods of improving target detection by processing of radar data are known, however the amount of processing that can be done on signals from a low-cost radar system is limited.
One data processing method suitable for use with low-costs radar systems is CFAR (constant false-alarm rate) processing. In a typical implementation of CFAR processing, a rectangular window is scanned over a pixellated map of returns produced by a radar system and a detection threshold is set for each pixel in the map by reference to returns corresponding to pixels within a reference group of pixels containing a particular pixel under consideration, based on an assumed clutter distribution for the area under observation. Typical choices for the assumed clutter distribution are Rayleigh, exponential and K-distributions, or their appropriate counterparts in radar systems which generate a plurality of range profile measurements for a given range and then combine the measurements to provide within-beam integration gain.
A problem with CFAR processing performed on data corresponding to returns from radar or similar systems (e.g. lidar systems) is that high clutter returns can result in detection thresholds for some pixels (i.e. those corresponding to regions of high clutter return) being set at too high a level, resulting in some targets not being detected.